Machine-readable code is commonly used for a variety of applications that require some form of verification. For example, print monitoring systems are used to monitor printed matter in some types of paper/sheet handling systems and to make certain control decisions based upon the character of the printed matter. The following is a list of a few conmmon applications:
1. Print quality monitoring: A print monitoring system detects the precision with which the printing system has formed the printed matter and/or the consistency with which the matter is printed across the entire paper. For example, in a laser printing system a print monitoring system detects low-toner situations by recognizing degradation in the contrast of printer""s output.
2. Digit control: In an overnight package delivery system, preprinted multi-layered shipping receipts are filled out by the customer. The customer keeps one layer, the package recipient receives another layer with the package, and, typically, a few layers are retained for the carrier""s records. Such shipping receipts are typically printed with a package tracking number represented as an alpha-numeric sequence on the customer""s and recipient""s layers of the shipping receipt and encoded as a universal product code (UPC) or bar code symbol on at least one of the carrier""s layers of the shipping receipt. The carrier""s package tracking system assumes that the package tracking numbers on each layer of the shipping receipt are identical. In such situations, a print monitoring system ensures that the package tracking numbers of each layer match during assembly of the shipping receipt.
3. Sequence control: When mailing personalized advertising and when mailing bills, it is necessary to ensure that all pages of the mailing insert are combined into the proper envelope. This is especially important in the case of confidential information, such as credit card or phone bills. Even if sheet transfer and handling error rates are low, the risk that a wrong bill will be sent to a customer is so unacceptable that a print monitoring system should match each page with the envelope prior to insertion of the bill into that envelope.
4. Verification: There are applications where it is necessary to verify the contents of a particular medium. The machine readable code provides a means to verify the contents of the medium.
5. Matching: In many applications, there is a requirement that two media be matched. A machine readable code can be used to ensure the media are properly matched.
Historically, sequence control has involved closely monitoring the printers, feeders, cutters, folders/accumulators, inserters, and stackers for paper jams or other error conditions. With proper coordination, the right materials generated by the printers can be placed into the correct envelopes or accumulated into the proper packets or publications.
Especially in the case of mailing sensitive material, print monitoring systems have been developed to confirm the insertion of the correct printed matter contents into the correct envelope. To facilitate print monitoring, sequence control information is commnonly placed into the printed matter. For example, both checks and bills have identifying indicia, such as separate identification numbers or customer account numbers, at predetermined locations. The print monitoring system can detect these identifiers and use them as sequence control information to ensure the insertion of all pages of a given bill for a particular account number in a properly addressed envelope and to insure the exclusion of any extraneous pages.
More recently, the introduction of inexpensive production-speed laser printers has made it practical to personalize mailed marketing material, brochures, and other materials for a specific recipient. In these cases, sequence control is critical to avoid disclosure of confidential information to unintended recipients. Unfortunately, in this environment, the inclusion of explicit sequence control information on the printed matter is often unacceptable. For example, letters and marketing brochures with machine readable information at predicable locations will appear, at first glance, to be bills. Consequently, they will be unlikely to generate a favorable impression on the addressee.
The foregoing disadvantages of the prior art are addressed by a method and system for encoding, on an imprintable medium, information identifying the imprintable medium in a manner detectable by a print-monitoring system. In the method of the invention, a print-control region is first defined on the imprintable medium. Preferably, this print control region is spatially separated from any other information encoded on the imprintable medium
The method then includes the step of defining an identification pattern on the print-control region. The identification pattern includes plurality of locations that are selected to identify the imprintable medium. Generally, each location is a region in the print control region on which information corresponding to one character is imprinted. The location can be contiguous or it can be discontinuous and dispersed throughout the print control region in order to reduce the likelihood of unrecoverable errors caused by imperfections in the medium.
The identification information is then placed upon the imprintable medium by imprinting, at each of the locations, one or more bit characters detectable by the print-monitoring system. Thus, each location includes one or more bit characters. The union of bit characters in a particular location designates a particular character. This enables the identification pattern to be detected and decoded by a printmonitoring system.
In the preferred embodiment, the print-control region is defined to be a rectangle having a first comer at a pre-determined location on the imprintable medium. In order to assist the print-monitoring system in locating the print-control region, it is preferable to imprint a first framing bit character at the first corner of the print-control region. In order to assist the print-control system in determining the size and extent of the print-control region, the method optionally includes the step of imprinting a second framing bit character at a second corner diagonally opposite the first comer of the print-control region.
The step of defining an identification pattern typically includes the step of defining a sequence of identification characters indicative of the identity of the imprintable medium. Each identifying character is assigned a location in the print-control region. To assist the print-monitoring system in correcting for printing errors, a check character is appended to each of the identification characters so that error correction can be readily be performed. In order to further assist the print-monitoring system in correcting errors, the bit characters used to represent each identifying character can be dispersed throughout the print-control region. By dispersing the bit characters in this manner, the likelihood that any one identifying character will not be irretrievably corrupted by multiple printing errors is significantly reduced.
In the preferred embodiment, the print-control region is a rectangular region having an array of rows and columns, each of which intersects at a slot. In this embodiment, the step of imprinting bit characters on the imprintable medium includes the step of imprinting the bit characters at locations defined by these slots. The resulting array of bit characters organized into rows and columns facilitates decoding by the print monitoring system. Additional error checking is provided by reserving a plurality of parity check slots in the ordered array and imprinting in those reserved parity check-slots a parity-setting bit character, the value of which is selected on the basis of the parity associated with each row and each column.
The present invention is directed to a non-intrusive data encoding technique in which a symbol representative of the data to be encoded on printed matter is detectable only upon close inspection, and is not readily apparent to the intended reviewer of the printed matter. By non-intrusive, it is meant that an observer scanning the printed information content will, more likely than not, fail to recognize the existence of the symbol representative of data to be encoded.
In other embodiments, however, the symbol is rendered substantially invisible to an unaided observer, even upon close inspection of the printed matter. A further advantage is that the symbol can be localized in the printed matter, thereby limiting the size of the image capture device required for detection and the computational burden on any associated processor. In the context of this application, the word xe2x80x9clocalizedxe2x80x9d is intended to refer to the designation of a particular region on the printed document that is dedicated to the task of receiving the symbol representative of information to be encoded.
Moreover, the symbol can be located in substantially the same location even between different printing runs of different printed matter. This feature can lower or eliminate the time required to recalibrate the image capture device""s position relative to the printed matter.
In general, according to one aspect, the invention concerns printed matter having, printed informational content and a print control symbol. The printed informational content is that content of a given document which is relevant to the intended reviewer, e.g., the printed text of the letter or pictures. The print control symbol is a symbol located at a predetermined position on the printed matter separate from the printed informational content. The print control symbol is hidden such that it is not readily apparent to a reviewer of the printed matter. Typically, the print control symbol encodes information concerning the printed matter, such as sequencing information, which is relevant to the printing system during printing and mailing.
In specific embodiments, the print control symbol comprises a series of bit characters. Preferably, these bit characters are organized into a two-dimensional matrix. The presence or absence of bit characters in the slots or elements of this matrix encodes binary data.
In order to minimize the visual impact of the print control symbol, the bit characters are made as small as possible. Preferably, each bit character is formed from only a few pels of the printer, with imaging capability and minimum web speeds being the limitation on the minimum size of the characters. With current, commercially feasible imaging equipment, the minimum size of the characters is about 0.051 millimeters (mm), although characters as small as 0.025 mm or even smaller can be used in certain applications. On the other end of the spectrum, characters as large as 0.25 mm will be sufficiently inconspicuous for use in certain other applications. Currently, the print characters being used are 0.085 mm in size. The minimum spacing between the centers of adjacent characters is about 0.2-0.4 mm, and more preferably, 0.25 mm. More generally, the spacing is 2-4 times the character size. The variation in relative spacing is about 15%. In a 300 dots per inch (DPI) laser printer, each bit character consists of one. In a 400 DPI printer, each bit characters consist of four pels in a 2xc3x972 square matrix; and in a 600 DPI printer, each bit character can include nine pels in a 3xc3x973 square matrix.
Further, in order to enable accurate decoding by the print monitoring system, the print control symbol preferably comprises data bit characters for encoding not only the print sequencing information, but also error correction information.
In other applications, the principles of the invention are used even where the print control symbol is apparent to the reader. In these applications, the bit characters can be made much larger.
Although the preferred embodiment of the invention concerns laser printing on paper or similar material, the principles of the invention have broader applicability and can readily be adapted to other forms of printed matter. Among the diverse materials that can be readily imprinted according to the principles of the invention are semiconductors, glassware, and fabrics.
According to another aspect, the invention also features a method for imprinting information on printed matter. In the method of the invention, printed informational content and print control symbols are both imprinted at predetermined positions on the printed matter. The print control symbol, which encodes sequencing information, is spatially separated from the printed informational content. In general, according to still another aspect, the invention also includes a printing system for imprinting sequence control information on printed matter. This printing system includes a printer that generates printed matter on which is imprinted printed informational content of interest to a human reviewer and a print control symbol for encoding sequence control information.
In preferred embodiments, the printer prints the print control symbol at predetermined positions on the printed matter. These positions are spatially separated from the informational content of the printed matter. The print control symbol itself is configured to be relatively inconspicuous to an unaided human reviewer. Preferably the print control symbol is invisible to the overwhelming majority of unaided human reviewers.
Finally, according to another aspect of the invention, the invention also features a print monitoring method and system.
The print monitoring method comprises generating printed matter that includes both printed informational content and a print control symbol. The print control symbol is then detected and decoded. The information contained in the now decoded print control system is then used to sequence the printed matter.
A printed matter monitoring system includes an image capture device and controller. The image capture device reads at least the print control symbol from the printed matter from the printer and the controller decodes data encoded in the print control system and makes sequencing decisions based upon that decoded data.